1. Field of the Related Art
The present invention relates to an image forming apparatus and an image forming method, and, more particularly to an image forming apparatus and an image forming method that can reduce a waste toner after transfer.
2. Description of the Related Art
In recent years, a reduction in size and improvement of an image quality of electrophotographic apparatuses have advanced and the electrophotographic apparatuses have been used in various places and applications. According to the reduction in size and the improvement of an image quality, importance of replacement work for consumables and maintenance work such as replacement of components has also been increasing. Maintenance most frequently performed by users in the electrophotographic apparatuses is replacement work for toner cartridges followed by disposal of waste toners.
When the users dispose of waste toners, it is likely that soil due to the toners occurs in the work. Moreover, generation of wastes as waste toners adversely affects the environment and is not economically efficient. In this way, the disposal of waste toners gives a negative image for both the users and the society in general.
Thus, as a form specialized in easy maintenance, there is a form of unitizing plural sections of an electrophotographic apparatus with relatively high frequency of maintenance and replacing the sections as a cartridge. In this unitization, a photosensitive member, a developing device, a cleaner, a waste toner box, and the like are unitized as a process unit integrally constituted. This process unit is constituted to be detachably attachable to an image forming apparatus. Consequently, a user intending to perform disposal of a waste toner can dispose of the waste toner simply by replacing the process unit periodically.
However, such a cartridge system also has a problem. Since the process unit is entirely replaced, even components that have not reached the end of replacement cycles and are still usable are replaced with other components.
For example, in the case of a cartridge in which a photosensitive member, a charger, and a cleaner are integrated, if the cleaner are worn, even if the photosensitive member is still usable, all the components are replaced. As a result, cost of consumables increases.
Moreover, in recent years, according to the appearance of a photosensitive member using α-Si and an organic photosensitive member provided with a surface layer with high hardness on the surface thereof, a replacement cycle of the photosensitive member has become longer. On the other hand, in order to extend a life of the cleaner to make a replacement cycle thereof longer, a structure of the cleaner itself is inevitably complicated. Therefore, a size of the cleaner is increased, making it difficult to apply the cleaner to a photosensitive member having a small diameter.
Thus, in a patent document 1 (JP-A-6-118857) and a patent document 2 (JP-A-10-31404), a method of detachably attaching a cleaner to a photosensitive member to allow a user to easily replace the cleaner is proposed.
However, even if the cleaner is replaced in this way, when an amount of waste toner is large, frequency of replacement of the cleaner has to be increased, a size of a cleaner unit itself has to be increased, or the cleaner and a waste toner tank have to be arranged separately to replace only the waste toner tank. Therefore, the problem described above is not still solved.
Further, considering that there is no problem if a waste toner is not generated, a waste-tonerless process is also proposed. In a patent document 3 (U.S. Pat. No. 4,727,395), a technique for collecting a transfer residual toner in a developing device without cleaning the transfer residual toner to prevent a waste toner from being generated is disclosed.
This is a system referred to as a cleanerless process. However, this system has a problem in that a high image quality is not obtained because a transfer residual toner is a hindrance at the time of exposure. Moreover, paper powder or dust may be mixed in the transfer residual toner. If the paper powder or the dust mixed in the transfer residual toner entirely enters a developing device, the paper powder or the dust could cause deterioration in an image quality. Since the transfer residual toner contains a large quantity of toner with poor performance that could not eventually be transferred, if the toner is entirely collected in the developing device, like the paper powder and the like, the toner causes deterioration in an image quality later.
In a patent document 4 (JP-A-2002-6630), a technique for actively depositing a toner uniformly on a photosensitive member after transfer in order to reduce deterioration in an image quality due to an exposure failure caused by a transfer residual toner is disclosed. In this method, since the toner is uniformly deposited on the photosensitive member, image unevenness undoubtedly becomes less conspicuous.
However, ideally, it is preferable that an amount of toner adhering to a photosensitive member is smaller. Thus, the method of intentionally depositing the toner on the photosensitive member is against the original form of use of the toner. It cannot be said that the method is an efficient method of use of the toner and is a positive solution as measures against deterioration in an image quality due to a residual toner.
In a patent document 5 (JP-A-9-251264), an example in which only a toner with polarity thereof inversed of a transfer residual toner is collected by a bias and a toner charged in a regular polarity is used in a cleanerless process is disclosed. However, in this method, since only the toner inversely charged can be collected, if an amount of transfer residual toner of the regular polarity is simply large, since the toner cannot be collected by a cleaner, image memory occurs to deteriorate an image quality.